Effect of Early Competition on Growth of Common Milkweed

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Abstract
Four modes of competition were studied in relation to early development of common milkweed (Asclepias syriacaL.) alone and in competition with green foxtail [Setaria viridis(L.) Beauv], redroot pigweed (Amaranthus retroflexusL.), and sorghum [Sorghum bicolor(L.) Moench ‘RS-626’]. The three species were used to study the effect of no competition, light competition, soil competition, and light and soil (full) competition on common milkweed. Common milkweed height was significantly reduced by soil and full competition with the three species, while only green foxtail caused a significant reduction in height due to light competition. Shoot weight of common milkweed was significantly reduced by light, soil, and full competition by the three species. Reproduction percentage of common milkweed roots was most severely reduced by light and full competition from green foxtail and redroot pigweed. An environment conducive to the establishment of the perennial common milkweed from seed exists when annual weeds are removed by herbicides.